As one example of uses of porous ceramic for slide member, there is (mechanical) seal ring used for a mechanical seal. A mechanical seal is one of shaft seal devices for fluid equipment designed for fluid-tight seal of rotating parts of various machineries, which is composed of a driven ring capable of moving in an axial direction according to abrasion of sliding surface, and a stationary sheet ring, and has a mechanism for buffering vibrations, and functions to limit fluid leakage on the sliding surface substantially perpendicular to a shaft relatively rotating.
In the mechanical seal, as a basic structure thereof is shown in FIG. 1, a sheet ring 5 and a driven ring 6 are installed between a rotating shaft 1 and a casing 2. Further, sliding surface 3 onto which a sealing action is applied form a plane perpendicular to the rotating shaft 1 by confronting surface of the sheet ring 5 serving as a stationary member and the driven ring 6 serving as a rotating member to perform a sealing action. The driven ring 6 is supported in a shock-absorbing manner by a packing 7 so as to not contact the rotating shaft 1.
A collar 9 is fitted in the rotating shaft 1, and is fixed to the rotating shaft 1 with a setscrew 10. A coil spring 8 is provided to be wound around the rotating shaft 1 between the collar 9 and the packing 7. The driven ring 6 and the collar 9 are prevented from rotating relatively each other by a spring-back force of the coil spring 8, and the driven ring 6 can be moved only in an axial direction.
Both of the side end face of the sheet ring 6 and the side end face of the driven ring 6 are substantially perpendicular to the axis of the rotating shaft 1, and these faces form the sliding surface 3 whose surface roughness and flatness are reduced by lapping.
A fluid to be sealed is supplied from the exterior, and a part thereof penetrates into a microspace formed with the respective sliding surface 3 to act as a lubricant. The respective sliding surface 3 is configured to slidingly contact one another by a spring-back force of the coil spring 8.
A shock absorbing rubber 4 supports the sheet ring 5 in a shock absorbing manner from the inside of the casing 2, and further prevents the lubricant penetrating into the microspace from leaking to the inner circumference of the seal ring during a rotation of the rotating shaft 1. When the rotating shaft 1 rotates, the collar 9 is rotated, and the driven ring 6 as well is rotated via the coil spring 8 and the packing 7.
The sliding surface 3 is abraded away by friction caused in accordance with a rotation. However, a state in which the driven ring 6 is pressured to contact the sheet ring 5 is retained, which holds the adherence between the sliding surface 3. The vibration of the rotating shaft 1 onto the sliding surface 3 is absorbed by the shock-absorbing rubber 4 and the packing 7 to be hardly transmitted. The mechanical seal is comprised of the above-described structure, and the sheet ring 5 and the driven ring 6 are generally called (mechanical) seal rings.
As members for seal rings used here, for example, carbon material, cemented carbide, silicon carbide ceramic, alumina ceramic, and the like are mainly used. In recent years, a container has been increased in which silicon carbide ceramic whose coefficient of friction during sliding is low and whose smoothness is excellent is used.
Further, among the silicon carbide ceramic, porous silicon carbide ceramic in which pores are formed by using a pore forming agent during the steps of preparing the silicon carbide ceramic for the purpose of improving a sliding property, has drawn attention.
For example, in patent Document No. 1, there has been proposed a silicon carbide seal ring containing independent pores having a mean pore size of 10 to 40 μm to have a porosity of 3 to 13% by volume by using emulsion-polymerized polystyrene beads serving as a pore forming agent.
In patent Document No. 2, there has been proposed a silicon carbide seal ring in which independent pores having a mean pore size of 50 to 500 μm are formed to have a porosity in the range from 2 to 12% by volume by using crosslinkable polystyrene beads, crosslinkable polymethyl methacrylate beads, crosslinkable polyethylene beads, or the like as a pore forming agent.
In patent Document No. 3, there has been proposed a ceramic sliding device formed of porous ceramic in which independent open pore having a mean pore size of 5 to 30 μm is provided in sliding-contact surface between ceramic slide member, actual sliding area ratios of optionally selected 10 the sliding-contact surface is 40 to 90%, and a standard deviation value of the actual sliding area ratios of the 10 areas is from 4 to 10%, and a porosity measured by an Archimedes' principle is 4% or less.    Patent Document No. 1: Japanese Unexamined Patent Publication No. 05-69066    Patent Document No. 2: U.S. Pat. No. 5,395,807    Patent Document No. 3: Japanese Patent No. 3,481,774